The present invention, in some embodiments thereof, relates to method and system for detecting interferences and, more particularly, but not exclusively, to method and system for detecting interferences in wireless communication.
The reduction or prevention of interference between various communication networks, such as civilian and government communication and navigation systems, is a continuing challenge to operators of wireless systems. In some regions, it is required by regulations to ensure that wireless access equipment does not interfere with certain radar systems in the 5 GHz band. In case radar is being detected, the wireless access network should move automatically to a frequency that does not interfere with the radar system. In some regions and bands like 900 MHz, 2.4 GHz, 2.5 GHz, 3.6 GHz, 5.x GHz and the like there is a media sharing by some operators and/or systems. In this case, interference detection and mitigation is required to ensure the service to the users by selection of a more quite frequency.
This challenge also exists in duplex communication systems in which a single duplex communication channel is used for transmitting and receiving a signal having a plurality of frames each comprising an uplink (UL) and a downlink (DL) sub frames, for example time division duplexing (TDD) systems. For clarity, TDD systems are based on an application of time-division multiplexing to separate outward and return signals. Using the TDD communication, a single frequency channel is assigned to both the transmitter and the receiver. Both the UL and DL traffic use the same frequency but at different times. In effect, TDD divides the data stream into frames and, within each frame, assigns different time slots to the forward and reverse transmissions. The TDD scheme may allocate the amount of time slots assigned to UL and DL in a dynamic and/or static manner. It should be noted that when the TDD communication is used for providing communication in a point to multi point services, such as local phone, internet access and the like, longer time slots are allocated for receiving DL transmission then for transmitting UL data. For example, the DL/UL ratio defined in IEEE 802.16 Standard allows a maximum UL ratio is limited to a ratio of 26:21 where the actual used TDD ratio is 29:18 that allows: 60% DL and 40% UL.
The requirement to detect radar signals and adjust communication accordingly is expressed in the communication standards, for example in standard 802.11, which is a set of standards created by the institute of electrical and electronics engineers (IEEE), govern wireless networking transmission methods and have several versions, such as the well-known 802.11a-g, which are used to provide wireless connectivity. An amendment to the 802.11 standard, called 802.11h, prevents wireless networks from obstructing radar, earth exploration satellite service (EESS), and space research service (SRS) transmission. The 802.11h amendment calls for, among other things, wireless local area networks (WLANs) and other devices to detect the presence of radar activity and to protect them from interference by avoiding operation on their communication channel or reducing transmission power.
In another standard, ETSI EN 301 893 V0.r, a dynamic frequency selection (DFS) mechanism is designed to detect and avoid operation in channels with radar activity. The DFS mechanism is fully controlled by an access unit (AU). When the DFS mechanism is enabled, the AU monitors the spectrum continuously, searching for signals with a specific pattern indication radar activity. Upon detecting radar activity, or interference activities the AU immediately informs the subscriber unit (SU), stops transmitting on this frequency and starts looking for another radar-free frequency.
It is possible that the CPE also will detect a Radar system and will try to move to other AU's frequency or will inform to the AU upon the Radar detection and will shut down for a while. The AU may use this information reported by the CPE to move to other not interfered frequency. The AU maintains a continuously updated database of all applicable frequencies, where each frequency is marked as Radar/Interferer Free, Radar/Interferer Detected or Adjacent to Radar/Interferer. The AU attempts to check a new frequency only if it is marked as Radar/Interferer Free. If a Radar/Interferer activity was detected on a certain frequency, it will be marked in the database as a Radar/Interferer Detected frequency. The AU will not attempt to check for radar activity in frequencies marked as Radar Detected. A certain time after detecting radar activity on a frequency, it will be removed from the list of Radar/Interferer Detected frequencies and will be marked as Radar/Interferer Free.
There are solutions for handling these interferences. For example as described in US Patent Application Pub. No. 2009/0086684, published on Apr. 2, 2009 that describes a method for preventing co-channel operation with a radar system includes the steps of setting a state of a first communication channel to active, connecting to a first wireless access point on the first communication channel, passively scanning at least a second communication channel for communication from a second wireless access point, setting a state of the second channel to active if frames are received on the second channel, determining whether an elapsed time since frames were received on at least one of the first channel and the second channel has exceeded a predefined value, and in response to the predefined value being exceeded for at least one of the first channel and the second channel, setting the state of a corresponding one of the first channel and the second channel to passive.